1. Field of the Invention
The invention relates to a device for optically capturing objects, having a support surface on whose first side an object can be placed.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.97
Such devices also have, in addition to a support surface, a light source for illuminating the first side of the support surface and a capturing means for optically capturing an object placed on the first side of the support surface. When the device is in the operating state, the capturing means and the light source are held by means of holders in a specific position relative to one another and relative to the support surface, the first side facing upwards and facing the light source and the capturing means.
Depending on the nature of the surface, the illuminating beams emitted by the light source are reflected in a diffuse manner in various directions by the support surface or are reflected in a directed manner in a specific direction with great intensity. In the case of directed reflection, the angle of reflection corresponds to the angle of incidence of the illuminating beams on the support surface. In certain positions of the light source and of the capturing means relative to the support surface, the support surface may have a region where illuminating beams are reflected in a directed manner in the direction of the capturing means. Illuminating beams reflected in a directed manner in the direction of the capturing means can reach intensities which considerably reduce the quality of the images of optically captured objects. These directed reflections are referred to as interference reflections or specular reflections.
By means of a suitable nature of the surface of the support surface—for example by means of a roughened surface provided with an appropriate coat of paint—it is known that it is possible to ensure that the illuminating beams are diffused in various directions. Thus, interference reflections caused directly by the surface of the support surface can be substantially prevented. If, however, an object having a surface reflecting in a highly directed manner, such as, for example, a printed product comprising high-gloss paper, a photograph or a foil, for example for an overhead projector, is placed flat on such a support surface and illuminated, the interference reflections may be so strong that optically capturing objects by the capturing means is no longer possible.
Interference reflections can be prevented in a manner known per se by choosing the distance of the light source from the capturing means or from the support surface to be appropriately large. However, a light source positioned so far away requires, as a rule, a plurality of light sources in order for a frequently required, uniform illumination of the support surface to be achieved. In addition, this remote positioning requires correspondingly large holding arms or booms, which leads to cumbersome and complicated devices.
European Patent Document EP 0 362 737 B1 discloses a device in which troublesome specular reflections are substantially avoided by means of illuminating beams which are projected via an objective and are aligned at small angles—in particular less than 2°—to the optical axis of the capturing means. This type of illumination requires—as described above—a large distance of the light source or capturing means from the support surface. This is achieved in this device by indirect projection of the illuminating beams or indirect focusing of the capturing beams by means of a mirror. Furthermore, an expensive projection objective coordinated with the light source is required in this device.